Method and Apparatus for Processing a Sheet Before the Sheet Transport in the Grip of Grippers

ABSTRACT

A method and an apparatus for improving the sheet transport in the grip of grippers in a sheet-processing machine, for example a printing press. The sheet corners of the print-free gripper edge are removed in order to increase the sheet stability and in order to avoid these limp sheet corners being able to turn over.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. § 119, of German application DE 10 2007 012 658.3, filed Mar. 16, 2007; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method for improving the sheet transport in a sheet-processing machine in which the sheet is gripped by means of gripper devices at a print-free edge and is passed on to following gripper devices.

In such sheet-processing machines, there is often the problem that the sheets are very limp at the corners of the leading sheet edge, in particular in the case of thin materials, and therefore tend to turn over.

In order to master this problem, attempts are generally made to support the sheet corners during the sheet transfer from one gripper system to the other.

German patent DE 196 05 420 C1 shows a gripper system in which blast air is blown from below against the sheet leading edge located in the grip of grippers, in order to support the unfixed sheet corners in order that the latter cannot turn over downward. The possibility, however, that the sheet corners turn over upward cannot be ruled out.

BRIEF SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method and an apparatus for processing a sheet prior to transport in a gripper, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which ensures that the sheet corners are prevented from turning over.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method for processing a sheet or sheet stack before transport in a grip of grippers through a sheet-processing machine, the method which comprises removing sheet corners at a leading edge of the sheet provided for gripping the sheet.

It is a particular advantage of the invention that the limp sheet corners that tend to turn over or bend over are removed before being transported through the sheet-processing machine. As a result of this measure, trouble-free sheet transport is ensured, which manages without additional means for stabilizing the sheet corners.

Preferably, in sheet-processing machines without sheet turning, only the sheet corners of the leading edge are removed. In machines with turning, for example a rotary perfecting machine, the sheet corners of the trailing edge are also removed as well.

In either case, in accordance with an added feature of the invention, the sheet corners are removed only in a region of a print-free edge of the sheet.

In accordance with another feature of the invention, the sheet corners are removed in a pre-stacking device or in a feeder of a sheet-processing machine.

With the above and other objects in view there is also provided, in accordance with the invention, an apparatus for carrying out the above method, i.e., an apparatus for processing a sheet or sheet stack prior to transport in a grip of grippers through a sheet-processing machine. The apparatus comprises a paper-milling device mounted on a vertical guide for up and down movement thereof.

In accordance with again another feature of the invention, there are provided two vertical guides assigned to a sheet leading edge and adjustably disposed for freely adjusting a format transversely with respect to a sheet transport direction. In accordance with a further feature of the invention, there are also provided vertical

guides assigned to a sheet trailing edge and adjustably disposed for freely adjusting a format transversely with respect to the sheet transport direction.

The removal of the sheet corners is preferably carried out in a pre-stacking station which, for example, is arranged upstream of the sheet stack of a feeder. Alternatively, however, the removal can also be carried out directly at the sheet stack of the feeder.

In other words, the apparatus provided for removing the sheet corners is, for example, a paper mill, which is arranged on a vertical guide and mills off the sheet corner in the region of the print-free edge by the mill being moved along at right angles to the sheet stack edge. A mill is preferably provided for each vertical sheet stack edge. The guides together with the mills can be adjusted transversely with respect to the sheet transport direction, so that they can be set to every sheet format to be processed. The rear guides can also be adjusted in the sheet transport direction, so that these can also be set to format length.

In a preferred embodiment of the invention, the milling devices each include a cylindrical milling head. The milling head is mounted such that an angle thereof can be adjusted in a horizontal plane. In a preferred embodiment, the milling head is mounted to define an angle of a milling line less than 45°.

In accordance with a concomitant feature of the invention, each milling device is assigned an extraction device for removing paper scraps and sheet corners.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in method and apparatus for processing a sheet before the sheet transport in the grip of grippers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic side view of a rotary press in section;

FIG. 2 shows a plan view of a sheet stack;

FIG. 3 shows a side view of the sheet stack; and

FIG. 4 shows a plan view of a sheet with the printing area identified.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a sheet-processing machine, for example a printing press ball 1. The machine 1 has a feeder 2, at least one printing unit 3 and 4 and a delivery 6. Sheets 7 are removed from a sheet stack 8 and, separated or overlapping, are fed over a feed table 9 to the printing units 3 and 4. The printing units each contain, in a known way, a plate cylinder 11, 12. The plate cylinders 11, 12 each have a device 13, 14 for fixing flexible printing plates. Furthermore, each plate cylinder 11, 12 is assigned a device 16, 17 for fully automatic or semiautomatic printing plate exchange.

The sheet stack 8 rests on a stack board 10 that can be raised under control. The sheets 7 are removed from the top of the sheet stack 8 by means of what is known as a suction head 18 which, inter alia, has a number of lifting and dragging suckers 19, 21 for separating the sheets 7. Furthermore, blowing devices 22 for loosening the upper sheet layers and sensing elements 23 for stack tracking are provided. In order to align the sheet stack 8, in particular the upper sheets 7 of the sheet stack 8, a number of side and rear stops 24 are provided.

As seen in the sheet transport direction, a pre-stacking station 26 is arranged upstream of the sheet stack 8. Referring now to FIG. 2, the pre-stacking station 26 has milling devices 27, which are arranged such that they can be moved on vertical guides 29. The milling devices 27 each comprise a cylindrical milling head 32, which has a drive motor 33. The latter is fixed to a carriage 34, which can be moved up and down by means of a drive device. The drive device can, for example, be an electric motor, an electromagnetic linear drive, or an operating cylinder.

The vertical guides 29 are arranged such that they can be adjusted transversely with respect to the sheet transport direction, so that they can be set to each respective format to be processed. The milling heads 32 are mounted such that they can be swiveled horizontally, so that an angle of about 45° can be set, preferably an angle α<45°.

A sheet 7 which is to be processed and printed in the recto printing mode without turning, for example in a printing press, needs to be processed only at its leading edge 37. In this case, the sheet corners 37 a are cut off at an angle α=about 40°. The cut line 38 in this case reaches at most as far as a printing area 39. As a result of this measure, a sufficiently large gripper edge 41 remains for holding the sheet 7 by means of grippers 42 provided.

A sheet 7 which is processed for example in the turning operation (e.g., in recto-verso printing), in which therefore its rear edge becomes the leading edge after turning, must also be processed at its sheet trailing edge 43, i.e. the sheet corners 44, 46 of the sheet trailing edge 43 are removed before the processing in the sheet-processing machine, for example a printing press.

Of course, the sheet-milling devices for the rear sheet corners 44, 46 are also arranged such that their format can be adjusted.

Each milling device 27 is additionally equipped with an extraction device 47 for paper scraps and the sheet corners. 

1. A method for processing a sheet or sheet stack before transport in a grip of grippers through a sheet-processing machine, the method which comprises: removing sheet corners at a leading edge of the sheet provided for gripping the sheet.
 2. The method according to claim 1, which comprises removing the sheet corners only in a region of a print-free edge of the sheet.
 3. The method according to claim 1, which further comprises removing rear sheet corners at a trailing edge of the sheet provided to grip the sheet for sheet transport in a turning operation.
 4. The method according to claim 1, which comprises removing the sheet corners in a pre-stacking device or in a feeder of a sheet-processing machine.
 5. An apparatus for processing a sheet or sheet stack prior to transport in a grip of grippers through a sheet-processing machine, the apparatus comprising: a vertical guide; a paper-milling device mounted on said vertical guide for up and down movement thereof; said paper-milling device being disposed to remove sheet corners at a leading edge of the sheet provided for gripping the sheet.
 6. The apparatus according to claim 5, wherein said vertical guide is one of two guides assigned to a sheet leading edge and adjustably disposed for freely adjusting a format transversely with respect to a sheet transport direction.
 7. The apparatus according to claim 6, which further comprises guides assigned to a sheet trailing edge and adjustably disposed for freely adjusting a format transversely with respect to the sheet transport direction.
 8. The apparatus according to claim 5, wherein said milling devices each includes a cylindrical milling head, and said milling head is mounted such that an angle thereof can be adjusted in a horizontal plane.
 9. The apparatus according to claim 8, wherein said milling head is mounted to define an angle of a milling line less than 45°.
 10. The apparatus according to claim 5, wherein each milling device is assigned an extraction device for paper scraps and sheet corners.
 11. The apparatus according to claim 5, wherein the sheet-processing machine is a rotary press. 